The relationship between measurement of in vivo brain glutamate and markers of iron metabolism: A proton magnetic resonance spectroscopy study in healthy adults

Fundamental human studies which address associations between glutamate and iron metabolism are needed. Basic research reports associations between glutamate and iron metabolism. Human studies report sex differences in iron metabolism and glutamate concentrations, which suggest that these relationships may differ by sex. We hypothesised associations would be apparent between in vivo glutamate and peripheral markers of iron metabolism, and these associations would differ by sex. To test this, we recruited 40 healthy adults (20 men, 20 women) and measured (a) standard clinical biomarker concentrations for iron metabolism and (b) an in vivo proxy for glutamate concentration, glutamate with glutamine in relation to total creatine containing metabolites using proton magnetic resonance spectroscopy studies with a two‐dimensional chemical shift imaging slice, with voxels located in bilateral dorsolateral prefrontal cortices, anterior cingulate cortices and frontal white matter. Only the female group reported significant associations between peripheral markers of iron metabolism and Glx:tCr concentration: (a) right dorsolateral prefrontal cortex Glx:tCr associated positively with serum transferrin (r = .60, p = .006) and negatively with transferrin saturation (r = ?.62, p = .004) and (b) right frontal white matter Glx:tCr associated negatively with iron concentration (r = ?.59, p = .008) and transferrin saturation (r = ?.65, p = .002). Our results support associations between iron metabolism and our proxy for in vivo glutamate concentration (Glx:tCr). These associations were limited to women, suggesting a stronger regulatory control between iron and glutamate metabolism. These associations support additional fundamental research into the molecular mechanisms of this regulatory control.     

l-Glutamine and Whole Protein Restore First-Phase Insulin Response and Increase Glucagon-Like Peptide-1 in Type 2 Diabetes Patients

l-glutamine triggers glucagon-like peptide-1 (GLP-1) release from L cells in vitro and when ingested pre-meal, decreases postprandial glycaemia and increases circulating insulin and GLP-1 in type 2 diabetes (T2D) patients. We aimed to evaluate the effect of oral l-glutamine, compared with whole protein low in glutamine, on insulin response in well-controlled T2D patients. In a randomized study with a crossover design, T2D patients (n = 10, 6 men) aged 65.1 ± 5.8, with glycosylated hemoglobin (HbA1c) 6.6% ± 0.7% (48 ± 8 mmol/mol), received oral l-glutamine (25 g), protein (25 g) or water, followed by an intravenous glucose bolus (0.3 g/kg) and hyperglycemic glucose clamp for 2 h. Blood was frequently collected for analyses of glucose, serum insulin and plasma total and active GLP-1 and area under the curve of glucose, insulin, total and active GLP-1 excursions calculated. Treatments were tested 1–2 weeks apart. Both l-glutamine and protein increased first-phase insulin response (p ≤ 0.02). Protein (p = 0.05), but not l-glutamine (p = 0.2), increased second-phase insulin response. Total GLP-1 was increased by both l-glutamine and protein (p ≤ 0.02). We conclude that oral l-glutamine and whole protein are similarly effective in restoring first-phase insulin response in T2D patients. Larger studies are required to further investigate the utility of similar approaches in improving insulin response in diabetes.     

谷氨酰胺对实验性结肠炎BABL/C小鼠肠黏膜的修复作用

目的 探讨谷氨酰胺(Gln)对BALB/C小鼠实验性结肠炎的治疗作用及可能的机制。方法 将50只BALB/C小鼠分为正常对照组、模型对照组、5-ASA组、Gln组、Gln+5-ASA组。各实验性结肠炎组小鼠采用2,4,6-三硝基苯磺酸灌肠造模后,治疗组给予药物干预,观察疾病活动指数(disease activity index, DAI),取结肠组织行H-E染色病理组织学检查并积分,应用免疫组织化学技术检测小鼠结肠黏膜TNF-α、NF-κB、IL-10、IL-1β的表达。结果 模型组小鼠DAI评分明显升高、结肠黏膜呈明显的炎症变化,表现为急性炎症,如溃疡形成、单核细胞浸润等。结肠黏膜TNF-α、NF-κB、IL-1β的表达增多、IL-10表达减少;谷氨酰胺能减轻小鼠大肠黏膜炎症,在一定程度上起到治疗小鼠实验性结肠炎的目的,其疗效与5-ASA相当;其中谷氨酰胺联合5-ASA治疗效果最佳,与正常对照组比较差异无统计学意义。结论 谷氨酰胺可用于治疗BALB/C小鼠实验性结肠炎,其作用机制可能与促进肠黏膜细胞增殖、维护肠黏膜屏障、调节免疫功能、抑制NF-κB活化、降低TNF-α、IL-1β表达,升高IL-10的表达等有关,与5-ASA联用其治疗效果优于两者单独用药。     

Glutamine Improves Innate Immunity and Prevents Bacterial Enteroinvasion During Parenteral Nutrition

Background: Patients receiving parenteral nutrition (PN) are at increased risk of infectious complications compared with enteral feeding, which is in part explained by impaired mucosal immune function during PN. Adding glutamine (GLN) to PN has improved outcome in some clinical patient groups. Although GLN improves acquired mucosal immunity, its effect on innate mucosal immunity (defensins, mucus, lysozymes) has not been investigated. Methods: Forty‐eight hours following venous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 10), PN (n = 12), or PN + GLN (n = 13) for 5 days. Small intestine tissue and luminal fluid were collected for mucin 2 (MUC2), lysozyme, cryptdin 4 analysis, and luminal interleukin (IL)–4, IL‐10, and IL‐13 level measurement. Tissue was also harvested for ex vivo intestinal segment culture to assess tissue susceptibility to enteroinvasive Escherichia coli. Results: In both luminal and tissue samples, PN reduced MUC2 and lysozyme (P < .0001, respectively) compared with chow, whereas GLN addition increased MUC2 and lysozyme (luminal, P < .05; tissue, P < .0001, respectively) compared with PN alone. PN significantly suppressed cryptdin 4 expression, while GLN supplementation significantly enhanced expression. IL‐4, IL‐10, and IL‐13 decreased significantly with PN compared with chow, whereas GLN significantly increased these cytokines compared with PN. Functionally, bacterial invasion increased with PN compared with chow (P < .05), while GLN significantly decreased enteroinvasion to chow levels (P < .05). Conclusions: GLN‐supplemented PN improves innate immunity and resistance to bacterial mucosal invasion lost with PN alone. This work confirms a clinical rationale for providing glutamine for the protection of the intestinal mucosa.